teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
sascha@3177: public class InvPow
sascha@3177: extends      Function
sascha@3177: {
sascha@3181:     public static final Derivative DERIVATIVE =
sascha@3181:         new Derivative("Q'(W) = ((W-d)/a)^(1/c)/(c*(W-d))") {
sascha@3181: 
sascha@3181:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3181:             instantiate(double [] parameters)
sascha@3181:         {
sascha@3181:                   double  a = parameters[0];
sascha@3181:             final double  c = parameters[1];
sascha@3181:             final double  d = parameters[2];
sascha@3181:             final double _1a = 1d/a;
sascha@3181:             final double _1c = 1d/c;
sascha@3181: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3181:                 @Override
sascha@3181:                 public double value(double W) {
sascha@3181:                     double Wd = W-d;
sascha@3181:                     return Math.pow(Wd*_1a, _1c)/(c*Wd);
sascha@3181:                 }
sascha@3181:             };
sascha@3181:         }
sascha@3181:     };
sascha@3181: 
sascha@3177:     public static final Function INSTANCE = new InvPow();
sascha@3177: 
sascha@3177:     public InvPow() {
sascha@3181:         super(
sascha@3181:             "pow",
sascha@3181:             "Q(W) = ((W-d)/a)^(1/c)",
sascha@3181:             new String [] { "a", "c", "d" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double value(double W, double [] parameters) {
sascha@3181:         double a = parameters[0];
sascha@3181:         double c = parameters[1];
sascha@3181:         double d = parameters[2];
sascha@3181:         return Math.pow((W-d)/a, 1d/c);
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3181:     public double [] gradient(double W, double [] parameters) {
sascha@3181:         double a = parameters[0];
sascha@3181:         double c = parameters[1];
sascha@3181:         double d = parameters[2];
sascha@3181:         double _1c = 1d/c;
sascha@3181:         double Wdac = Math.pow((W-d)/a, 1d/c);
sascha@3181:         double Wd = W-d;
sascha@3181:         return new double [] {
sascha@3181:             -Wdac/(a*c),
sascha@3181:             (Wdac*Math.log(Wd/a))/(c*c),
sascha@3181:             -Wdac/(c*Wd)
sascha@3181:         };
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Derivative getDerivative() {
sascha@3177:         // TODO: Implement me!
sascha@3177:         return null;
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Function getInverse() {
sascha@3178:         return Pow.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :